This invention relates to thermoplastic resin compositions. More particularly, this invention relates to a thermoplastic resin composition that exhibits an excellent moldability, an excellent surface lubricity, and an excellent scratch and mar resistance. This invention also relates to moldings comprising this thermoplastic resin composition.
Thermoplastic resins offer the advantages of light weight and good corrosion resistance and as a consequence are used for interior and exterior components in automobiles and for the exterior components of household electrical appliances. However, these thermoplastic resins, and thermoplastic elastomers in particular, suffer from a poor surface lubricity and a poor wear or abrasion resistance, and it is fairly easy to scratch or mar the surface of moldings produced therefrom. In order to address these shortcomings in thermoplastic resins, quite a few compositions comprising polyorganosiloxane/thermoplastic elastomer blends have been disclosed. For example, Japanese Patent Application Laying Open Number Sho 60-76561 (76,561/1985) teaches a composition comprising the addition of silicone oil and polytetrafluoroethylene powder to polyolefin-type thermoplastic elastomer. This composition has an enhanced surface lubricity and an enhanced resistance to wear and abrasion. Japanese Patent Application Laying Open Number Hei 11-35750 (35,750/1999) teaches a composition comprising a blend of polyorganosiloxane having a viscosity of at least 100,000 centistokes in a polyolefin-type thermoplastic elastomer. Moldings obtained from the former composition, however, exhibit a number of drawbacks that derive from the fact that the silicone oil outmigrates to the surface thereof and the moldings can become sticky and they may suffer from a loss of aesthetics in their appearance due to an increased gloss. In addition, their surface lubricity can gradually decline during long-term use. In the case of the latter composition, it is difficult to achieve a uniform dispersion of the polyorganosiloxane in the polyolefin-type thermoplastic elastomer, which results in a poor blend stability. Moldings therefrom also suffer from a gradual decline in surface lubricity during long-term use. In addition, Japanese Patent Application Laying Open Number Hei 8-58043 (58,043/1996) teaches a composition obtained by blending polyolefin resin with calcium carbonate and organosiloxane-modified polyolefin resin. Japanese Patent Application Laying Open Number Hei 9-40841 (40,841/1997) teaches a composition comprising a blend of polyorganosiloxane-grafted acrylonitrile-styrene copolymer in acrylonitrile-butadiene-styrene copolymer (ABS resin). Unfortunately, moldings fabricated from these latter compositions suffer from an inadequate surface lubricity and scratch or mar resistance and as a result may not be fully satisfactory for some applications.
The object of this invention is to provide a thermoplastic resin composition that has an excellent moldability, an excellent surface lubricity, and an excellent scratch or mar resistance.
A thermoplastic resin composition comprising
(A) 100 weight parts thermoplastic resin,
(B) 0.1 to 100 weight parts of a mixture of
(b-1) thermoplastic resin and
(b-2) polyorganosiloxane that has a viscosity at 25xc2x0 C. of at least 1,000,000 mPaxc2x7s, and
(C) 0.1 to 100 weight parts polyorganosiloxane-bonded thermoplastic resin in which
(c-1) thermoplastic resin and
(c-2) polyorganosiloxane
are chemically bonded to each other.
This invention also relates to moldings obtained by the molding or forming of the thermoplastic resin composition.
The present invention is a thermoplastic resin composition comprising
(A) 100 weight parts thermoplastic resin,
(B) 0.1 to 100 weight parts of a mixture of
(b-1) thermoplastic resin and
(b-2) polyorganosiloxane that has a viscosity at 25xc2x0 C. of at least 1,000,000 mPaxc2x7s, and
(C) 0.1 to 100 weight parts polyorganosiloxane-bonded thermoplastic resin in which
(c-1) thermoplastic resin and
(c-2) polyorganosiloxane
are chemically bonded to each other.
This invention also relates to moldings obtained by the molding or forming of the present thermoplastic resin composition.
To explain the preceding in greater detail, the thermoplastic resin (A) may be any organic resin that, while occurring as a solid at ambient temperature, can undergo plastic deformation upon an increase in temperature. The type and other characteristics of this thermoplastic resin (A) are not otherwise critical. Within this broad range of permissible thermoplastic resins, the thermoplastic resins known as thermoplastic elastomers are preferred for (A). Thermoplastic elastomers are organic resins that exhibit rubbery elastic behavior at ambient temperature, but which can undergo plastic deformation upon an increase in temperature (see Jitsuyo Purasuchikku Jiten (English title: The Practical Plastic Encyclopedia), pages 180 to 207, published 1 May 1993 by Kabushiki Kaisha Sangyo Chosa-kai). These thermoplastic elastomers can be exemplified by polyolefin-type thermoplastic elastomers, polystyrene-type thermoplastic elastomers, polyamide-type thermoplastic elastomers, polyester-type thermoplastic elastomers, polyvinyl chloride-type thermoplastic elastomers, polyurethane-type thermoplastic elastomers, and fluoropolymer-type thermoplastic elastomers; among which the polyolefin-type thermoplastic elastomers, polystyrene-type thermoplastic elastomers, and polyester-type thermoplastic elastomers are preferred. The polyolefin-type thermoplastic elastomers are particularly preferred. The polyolefin-type thermoplastic elastomers include polymer copolymer-type thermoplastic elastomers and polymer blend-type thermoplastic elastomers in which the hard phase is polyethylene or polypropylene and the soft phase is EPDM, EPR, or butyl rubber. These polyolefin-type thermoplastic elastomers are available commercially under such product names, for example, as Mirastomer(copyright) and Goodmer, both from Mitsui Petrochemical Co., Ltd. The polystyrene-type thermoplastic elastomers include block polymer-type thermoplastic elastomers in which the hard phase is polystyrene and the soft phase is polybutadiene, polyisobutylene, or hydrogenated polybutadiene; these polystyrene-type thermoplastic elastomers are available commercially under such product names, for example, as Tuftec(copyright), Tufprene(copyright), Sorprene, and Asaprene(copyright), all from Asahi Chemical. The polyester-type thermoplastic elastomers include block polymer-type thermoplastic elastomers in which the hard phase is polyester and the soft phase is polyether or polyester. These polyester-type thermoplastic elastomers are available commercially, for example, under the product name Hytrel(copyright) from Du Pont-Toray Co., Ltd. Component (A) can be a single thermoplastic resin or thermoplastic elastomer or can be a mixture of 2 or more. Component (A) preferably has a Rockwell hardness (R scale) at 25xc2x0 C. no greater than 70 and preferably has a Shore D hardness (ASTM D2240) at 25xc2x0 C. no greater than 45.
Component (B) is an essential component that imparts moldability and surface lubricity to the present composition. The thermoplastic resin (b-1) encompassed by component (B) can be exemplified by polyolefin resins such as polyethylene (PE), low-density polyethylene (LDPE), high-density polyethylene, ultrahigh molecular weight polyethylene (UHMPE), polypropylene (PP), polymethylpentene (MPX), ethylene-(meth)acrylate ester copolymers, and ethylene-vinyl acetate copolymers (EVA); acrylic-type vinyl resins such as polymethyl methacrylate (PMMA); styrene-type vinyl resins such as polystyrene (PS), high-impact polystyrene (HIPS), acrylonitrile-butadiene-styrene (ABS) copolymers, acrylonitrile-styrene (AS) copolymers, acrylonitrile-acrylic rubber-styrene (AAS) copolymers, and acrylonitrile-ethylene/propylene rubber-styrene (AES) copolymers; other vinyl resins such as polyvinyl acetate, polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyvinyl alcohol (PVA), and polytetrafluoroethylene (PTFE); polyester resins such as polybutylene terephthalate (PBT) and polyethylene terephthalate (PET); polyamide resins such as nylon 6, nylon 66, nylon 610, nylon 11, and nylon 12; polyoxyalkylene resins such as polyacetal (POM); and other thermoplastic resins such as polycarbonates (PC), modified polyphenylene ethers (modified PPE), polyvinyl acetates (PVAC), polysulfones (PSU), polyethersulfones (PES), polyphenylene sulfides (PPS), polyarylates (PAR), polyamideimides (PAI), polyetherimides (PEI), polyetheretherketones (PEEK), polyimides (PI), and liquid-crystal polyesters (LCP), as well as copolymers of the preceding. Preferred among the preceding are thermoplastic resins that have a Rockwell hardness (R scale) at 25xc2x0 C. of at least 80. In addition, component (b-2) need not be compatible with component (A) as long as it can be microscopically dispersed in component (A).
Component (b-2), which is the other component encompassed by component (B), is an essential component that imparts moldability and surface lubricity to the present composition. This component (b-2) must have a viscosity at 25xc2x0 C. of at least 1,000,000 mPaxc2x7s and preferably has a viscosity of at least 5,000,000 mpaxc2x7s and more preferably of at least 10,000,000 mPaxc2x7s. Component (b-2) is preferably a gum with a Williams plasticity of at least 100, more preferably of at least 120, and most preferably of at least 150. Such a component (b-2) can be polyorganosiloxanes with the average unit formula R1aSiO(4-a)/2where R1 is a monovalent hydrocarbyl or halogenated monovalent hydrocarbyl and 1.8xe2x89xa6axe2x89xa62.2. The monovalent hydrocarbyl can be exemplified by alkyl such as methyl, ethyl, and propyl; cycloalkyl such as cyclopentyl and cyclohexyl; aryl such as phenyl and xylyl; and aralkyl such as benzyl, phenethyl, and 3-phenylpropyl. The halogenated hydrocarbyl can be exemplified by 3,3,3-trifluoropropyl and 3-chloropropyl. The polyorganosiloxane under consideration (b-2) can be specifically exemplified by polydimethylsiloxanes endblocked by trimethylsiloxy at both terminals, polydimethylsiloxanes endblocked by silanol at both terminals, polydimethylsiloxanes endblocked by silanol at only one terminal, polydimethylsiloxanes endblocked by methoxy at both terminals, dimethylsiloxane-methylphenylsiloxane copolymers endblocked by trimethylsiloxy at both terminals, dimethylsiloxane-methylphenylsiloxane copolymers endblocked by silanol at both terminals, dimethylsiloxane-diphenylsiloxane copolymers endblocked by trimethylsiloxy at both terminals, dimethylsiloxane-diphenylsiloxane copolymers endblocked by silanol at both terminals, and dimethylsiloxane-methyl(3,3,3-trifluoropropyl)siloxane copolymers endblocked by trimethylsiloxy at both terminals. In order to avoid staining of the mold or die during molding operations and prevent molding defects, component (b-2) preferably contains no more than 5,000 ppm and more preferably no more than 2,000 ppm low molecular weight organosiloxane having a vapor pressure greater than or equal to 10 mmHg at 200xc2x0 C.
Component (B) is a mixture of the above-described components (b-1) and (b-2). The mixing proportions of components (b-1) and (b-2) should provide a component (b-2) content in component (B) of from 1 to 80 weight % and preferably from 20 to 80 weight %.
Component (B) is used at from 0.1 to 100 weight parts per 100 weight parts component (A) and is preferably used at from 0.1 to 50 weight parts and more preferably at from 0.1 to 25 weight parts per 100 weight parts component (A). No effect from the addition of component (B) is seen at a component (B) addition below 0.1 weight part, while the scratch or mar resistance declines at a component (B) addition in excess of 100 weight parts.
Component (C) functions to enable a uniform dispersion of component (B) in component (A) and through this action functions to impart surface lubricity and scratch/mar resistance to the present composition. Component (C) is a thermoplastic resin in which component (c-1) is chemically bonded to component (c-2). Component (c-1) can be exemplified by the same thermoplastic resins as provided above for component (b-1), among which thermoplastic resins having a Rockwell hardness (R scale) at 25xc2x0 C. of at least 80 are preferred. The thermoplastic resins under consideration can be exemplified by polyolefin resins such as polypropylene resins and ethylene-propylene copolymers; polyamide resins such as nylon 6, nylon 66, and nylon 610; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; aromatic polycarbonate resins; and polyacetal resins. Preferred among these examples are polyolefin resins such as polypropylene resins and ethylene-propylene copolymers.
Component (c-2) is the other component in component (C) and can be a polyorganosiloxane with average unit formula R1aR2bSiO(4-a-b)/2 where R1 is monovalent hydrocarbyl or halogenated monovalent hydrocarbyl, R2 is C1 to C12 alkenyl, and a and b are positive numbers such that 0.0001xe2x89xa6a/bxe2x89xa60.1000 and 1.8xe2x89xa6a+b xe2x89xa62.2. The monovalent hydrocarbyl can be exemplified by alkyl such as methyl, ethyl, and propyl; cycloalkyl such as cyclopentyl and cyclohexyl; aryl such as phenyl and xylyl; and aralkyl such as benzyl, phenethyl, and 3-phenylpropyl. The halogenated hydrocarbyl can be exemplified by 3,3,3-trifluoropropyl and 3-chloropropyl. R2 can be exemplified by vinyl, propenyl, butenyl, pentenyl, hexenyl, and decenyl with vinyl and hexenyl being preferred. Hexenyl is particularly preferred for the good reactivity it affords. The viscosity of this polydiorganosiloxane at 25xc2x0 C. should be at least 1,000,000 mPaxc2x7s and is preferably at least 5,000,000 mPaxc2x7s and more preferably is at least 10,000,000 mPaxc2x7s. In order to avoid staining of the mold or die during molding operations and prevent molding defects, component (c-2) preferably contains no more than 5,000 ppm and more preferably no more than 2,000 ppm low molecular weight organosiloxane having a vapor pressure greater than or equal to 10 mmHg at 200xc2x0 C. The polyorganosiloxane under consideration can be exemplified by polydimethylsiloxanes endblocked at both terminals by dimethylvinylsiloxy, polydimethylsiloxanes endblocked at both terminals by dimethylhexenylsiloxy, dimethylsiloxane-methylhexenylsiloxane copolymers endblocked at both terminals by silanol, dimethylsiloxane-methylvinylsiloxane copolymers endblocked by silanol at only a single terminal, dimethylsiloxane-methylvinylsiloxane copolymers endblocked at both terminals by methoxy, dimethylsiloxane-methylhexenylsiloxane copolymers endblocked by trimethylsiloxy at both terminals, and dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymers endblocked at both terminals by trimethylsiloxy.
Component (C) can be synthesized, for example, by mixing component (c-1) with component (c-2) with heating (Japanese Laid Open (Kokai or Unexamined) Patent Application Number Hei 8-127660 (127,660/1996)). The reaction between components (c-1) and (c-2) can be promoted by the addition of those organoperoxides and inorganic peroxides familiar as radical generators. This mixing time is preferably from 1 minute up to 60 minutes. Mixing times longer than 60 minutes should be avoided because they can cause degradation of the thermoplastic resin. The mixing temperature should be in the range of from the melting point of the thermoplastic resin up to the decomposition temperature of the thermoplastic resin, and in general will be in the range from 140 to 260xc2x0 C.
The ratio between components (c-1) and (c-2) should provide a component (c-2) content in component (C) of from 1 to 80 weight % and preferably from 20 to 80 weight % and more preferably from 30 to 70 weight %.
Component (C) should be present at from 0.1 to 100 weight parts per 100 weight parts component (A) and is preferably present at from 0.1 to 50 weight parts and more preferably at from 0.1 to 25 weight parts per 100 weight parts component (A). No effect from the addition of component (C) is seen at a component (C) addition below 0.1 weight part, while the scratch or mar resistance declines at a component (C) addition in excess of 100 weight parts.
While the present composition comprises components (A) through (C) as described above, it may also contain a plate- or flake-form inorganic filler (D) in order to improve rigidity and dimensional stability. Component (D) can be exemplified by talc, mica, clay, kaolin, hydrotalcite, vermiculite, smectite, and glass flake. Component (D) is preferably added at from 1 to 100 weight parts and more preferably at from 5 to 80 weight parts for each 100 weight parts component (A).
The present composition may also contain an oxidation inhibitor at from 0.1 to 5 weight parts and preferably 0.1 to 2 weight parts oxidation inhibitor for each 100 weight parts of the composition. This oxidation inhibitor can be, for example, a hindered phenol or a hindered amine. The present composition may additionally contain epoxy resin, for example, a bisphenol A epoxy resin, at from 0.1 to 5 weight parts and preferably 0.2 to 3 weight parts epoxy resin for each 100 weight parts of the composition. The epoxy resin is used when it becomes necessary to prevent the diminution in activity caused by additive adsorption, for example, adsorption of the oxidation inhibitor by the inorganic filler.
The present composition may also contain, insofar as the object of the invention is not impaired, various other additives known for admixture into thermoplastic resin compositions. These additives include granular and irregularly shaped inorganic fillers such as calcium carbonate, barium sulfate, titanium oxide, zinc oxide, iron oxide, aluminum oxide, silicon dioxide, magnesium hydroxide, aluminum hydroxide, and carbon black; needle-shaped inorganic fillers such as wollastonite, potassium titanate, and magnesium sulfate; fibrous inorganic fillers such as glass fiber and carbon fiber; as well as UV absorbers; photostabilizers; heat stabilizers; plasticizers; blowing agents; crystal nucleating agents; lubricants; antistatics; agents that impart electrical conductivity; colorants such as dyes and pigments; compatibilizers; crosslinkers; flame retardants; antimolds; shrinkage reducers; thickeners; release agents; anticlouding agents; blueing agents; and silane coupling agents.
The present composition can be prepared simply by mixing components (A) to (C) to homogeneity. The apparatuses used for this preparation can be exemplified by Banbury mixers, kneader mixers, two-roll mills, and continuous compounding extruders.
The usual and well-known molding technologies can be used to produce moldings from the present composition, for example, injection molding, extrusion molding, and compression molding.
The present composition as described hereinabove is highly moldable and produces moldings that exhibit an excellent surface lubricity and an excellent resistance to scratching and marring. The present composition is therefore well-suited for application in those fields where such features are critical, for example, for interior and exterior automotive components such as door trim, console panels, instrument panels, and weather stripping, and for the exterior elements of household electrical appliances.
This invention will now be explained in greater detail in the following working examples. Parts in the working and comparative examples denotes weight parts. The values reported in the examples for the viscosity, Rockwell hardness, and Williams plasticity were measured at 25xc2x0 C. The Williams plasticity of the polyorganosiloxanes was measured by the method described below. Also described below are the methods used to evaluate (i) mold staining during molding, (ii) molded article appearance, (iii) scratch resistance, (iv) the appearance of the molding surface after durability testing, and (v) surface lubricity.
Measurement of the Williams plasticity
The Williams plasticity was measured according to the method described in JIS K6249:1997, xe2x80x9cTesting method for uncured and cured silicone rubbersxe2x80x9d. Specifically, 4.2 g of the polyorganopolysiloxane was made into a cylindrical test specimen; the test specimen was sandwiched between cellophane paper sheets and then placed in a dial gauge-equipped parallel plate plastometer (Williams plastometer from Ueshima Seisakusho Co., Ltd.); a load of 5 kg was applied; and after standing for 2 minutes the scale on the dial gauge was read to the millimeter level and the thickness of the test specimen was recorded. This numerical value was multiplied by 100 to obtain the value of the Williams plasticity.
Mold Staining During Molding and Molded Article Appearance
The thermoplastic resin composition was molded into a round plate using an injection molder. After the molding operation, the appearance of the surface of the mold and the appearance of the surface of the molded article were both evaluated by visual inspection.
Determination of Scratch Resistance
The scratch resistance was measured using a thrust friction wear tester from Toyo Seiki Seisakusho. A plate was first molded from the thermoplastic resin composition using an injection molder. Onto the surface of this plate was set a cylindrical stainless steel element that carried a nail-like projection whose end was rounded to a radius of 2 mm. After displacement of this element at a velocity of 2 cm/s under a load of 250 g/cm2 , the surface of the molding was inspected for the appearance of any scratching. This surface inspection was carried out by photographing the surface of the plate while exposing it to light from a fluorescent lamp at a 45xc2x0 angle of incidence. The resulting photograph was visually inspected in order to determine the presence/absence of scratching on the plate surface. The data are reported as relative values using 100 as the pre-test value.
Evaluation of the appearance of the molding surface after durability testing The molded plate used in measurement of the scratch resistance was held for 200 hours in an oven maintained at 50xc2x0 C., after which period of time it was removed and its surface was visually evaluated. A score of xe2x80x9cglossyxe2x80x9d was rendered when gloss had been produced due to bleed out by the silicone component; a score of xe2x80x9cnonglossyxe2x80x9d was rendered in the absence of this gloss.
Surface Lubricity
The surface lubricity was evaluated through measurement of the dynamic coefficient of friction (COF) of a molding fabricated from the thermoplastic resin composition. Cylindrical moldings were fabricated from polypropylene resin (MI (230xc2x0 C., 2.16 kgf)=11 g/10 min) and the thermoplastic resin composition using an injection molder. Using these moldings as test specimens, the dynamic COF was measured by friction testing under a load of 250 g/cm2 at a velocity of 2 cm/s.